The present invention relates to cost control in a telecommunications system and more particularly to cost control in a mobile telecommunications system.
In today's mobile telecommunications networks, the operator of a mobile network is able to maintain tight control over the calls made and services used by its subscribers when they are at home, i.e. when they are registered with the operator's own network. For example, if a subscriber exceeds his calling credit limit the operator can notify the subscriber of this situation and/or can prevent the subscriber from making further calls until his outstanding account is settled. Similarly, where a subscriber makes use of a top-up account, e.g. using scratch cards to credit his account, an operator can restrict the subscriber's access when the subscriber's credit drops to zero.
Such charging control is possible because the Mobile Switching Centre (MSC) which acts as the “local exchange” for a subscriber sends Call Detail Records (CDRs) at regular intervals to a charging node of the subscriber's home network. However, this is only possible when the serving MSC is an MSC of the home network. In the event that a mobile subscriber is registered with an MSC of a foreign network (i.e. the subscriber is “roaming”), CDRs generated by the MSC are passed to a home network through a clearing house in so-called TAP files (if necessary, multiple CDRs are collated in the foreign network and the collated CDRs are sent to the clearing house in a single TAP file). It can take at least two days or even more before the CDRs are forwarded on to the home network.
A home network cannot therefore monitor, in real time or near real time, the charges being incurred by one of its subscribers when that subscriber is roaming in a foreign network. Rather, charging information is only sent periodically from the foreign network to the home network (e.g. every few days). There therefore exists a possibility that fraud by a roaming subscriber will go undetected by the subscriber's home network for some time, and that during that time the home network operator will incur considerable losses. Furthermore, even though CDRs can be generated periodically for a subscriber when that subscriber is registered with his home network, the use of exchanges which generate CDRs at fixed regular intervals for all registered subscribers represents a non-optimal solution as the fixed interval may be too long for certain classes of subscribers and too short for others, and can unnecessarily increase the computational load in the serving exchange.
In order to overcome this problem, a protocol referred to as Customised Applications for Mobile network Enhanced Logic (CAMEL) has been standardised by ETSI (further enhancements to CAMEL are in the process of being standardised—3GPP). CAMEL provides for the transfer of charging related information in near real time between the home network (the “controlling” network) and a foreign network (the “serving” network) in which a subscriber of the home network is roaming. In particular, CAMEL enables a home network to authorise a roaming subscriber for a fixed time period at the end of which the foreign network must seek a new authorisation for the subscriber. It will be appreciated that the main application of CAMEL is in respect of pre-paid subscribers.
In the future, billing for mobile services is likely to be made on the basis of criteria other than simply time and call destination (or origin). For example, with the introduction of packet switched data services such the GSM phase 2 enhancement known as General Packet Radio Service (GPRS), it may be appropriate to charge subscribers on the basis of data volume sent (or received) and the destination (or source) of the data.
According to the current CAMEL proposal to control GPRS, the serving node (i.e. the Serving GPRS Support Node (SGSN)) for a given subscriber will simultaneously monitor a data connection established by a subscriber vis-a-vis call time and sent data volume. The serving node uses time and data volume limits (previously received from the subscriber's home network) to trigger the sending of respective new authorisation requests to the home network. Time and data volume are treated independently of one another resulting in a large volume of charging related signalling information being sent back and forth between the foreign network and the home network. The more charging criteria are used, the greater will be the volume of charging related signalling information. Signalling traffic represents a significant cost factor for network operators, and the current CAMEL proposal is therefore not optimal.